Ionic mechanisms of the rapid (nicotinic) phase of the acetylcholine response of identified Planorbis neurons

: The response to electrophoretic application of acetylcholine and suberyldicholine was studied in two identified neurons (LPed-2 and LPed-3) isolated from Planorbarius corneus left pedal ganglion. Acetylcholine reversal potential was found to be significantly more negative with K(2)SO(4)-filled microelectrodes than with KCl-filled ones. Reversal potentials for both acetylcholine and suberyldicholine were shifted in the depolarizing direction when Cl- in external medium was partly replaced by SO(2-)(4). These results suggest the Cl--dependence of both acetylcholine and suberyldicholine responses in LPed-2 and LPed-3. Both reversal potentials are identical (-50 mV) in LPed-3, whereas in LPed-2 the acetylcholine reversal potential was significantly less negative (-46 mV comparing to -62 mV). Partial substitution of sodium ions by tris shifted the acetylcholine reversal potential (but not the reversal potential of suberyldicholine) towards the hyperpolarization in LPed-2. Benzohexonium produced the same effect. The conclusion is made that in LPed-2 acetylcholine activates cholinoreceptors controlling Na;ermeability, besides cholinoreceptors responsible for Cl- permeability, whereas suberyldicholine activates selectively only cholinoreceptors controlling Cl- permeability.